Github actions - variables

Question

I am new to GitHub action and I am trying to pull a variable from a file but I cannot get it to work. Could anyone help, please?

Also I want my default version always to be the latest. You can set that to update in terraform but I can't find the AWS CLI command

  deploy:
    runs-on: ubuntu-latest
    steps:
      - run: aws ec2 modify-launch-template --launch-template-id $LAUNCH-TEMPLATE-ID --default-version 3
        with:
          varFile: 'fr-stage-variables.json'